Intricate Spin‐Vibronic Dynamics and Excited‐State Intramolecular Thiol Proton Transfer in Dithiotropolone

We perform a computational investigation to unravel the mechanisms of intramolecular thiol proton transfer and triplet formation in dithiotropolone. The S₁ and S₂ states are dipole-forbidden, whereas S₃ and S₄ are dipole-allowed states in this molecule. Upon initiating the nuclear wavepacket on S₃, this molecule exhibits simultaneous S₃ to S₂/S₁ internal conversion and S₃-T₄ intersystem crossing. Further simulations reveal that the molecule shows ultrafast internal conversion in the triplet manifold, similar to its singlet dynamics. Apart from these decay processes in the Franck-Condon region, this molecule can display thiol proton transfer via multiple singlet states due to low barrier energies along the reaction coordinate. The S₁-T₄ and S₃-T₅/T₆ crossings upon the S-H coordinate's elongation illustrate that the molecule can also show the triplet formation outside the Franck-Condon region.